This invention relates to a method of joining multiple plates together to form a unitary coherent stack of plates. The invention has applicability in the formation of rotors for electric motors, wherein the rotor comprises a stack of plates laminated together along the rotor's axial dimension. Typically, the rotor is comprised of about sixty steel plates, having a diameter of about three inches and an individual plate thickness of about 0.025 inch. The axial length of the formed rotor is about one and one-half inches.
Under this invention, the plates are held together solely by means of integral projections extending from each plate into mating recesses formed in an adjacent plate. Reciprocating dies (punches) are used to simultaneously form a projection on one face of each plate and a recess on the other face of the plate. The plates are individually added to a stack of plates, with the projections on each newly added plate nested into recesses in the end plate in the stack.
As each plate is added to the stack of plates, a restriking die is actuated to form notches in the exposed face of the newly added plate. The plate material in axial alignment with each notch is extruded into a registering notch in the end plate of the stack so as to form a frictional connection between the newly added plate and the stack of plates. The restriking (notching) process is employed as each plate is added to the stack.
It has been proposed to laminate plates together, using integral projections and recesses in opposite surfaces of the plates. Prior art of interest includes U.S. Pat. No. 2,975,312 to W. J. Ploran; U.S. Pat. No. 3,202,851 to W. Zimmerle, et al; U.S. Pat. No. 4,280,275 to Y. Mitsui; U.S. Pat. No. 4,760,632 to E. Rapp; and U.S. Pat. No. 2,254,588 to J. Williams.
The present invention is believed to represent an improvement over the art in the addition of a restriking (notching) step for increasing the frictional adherence between the plates.